Preheat oven to 350 degrees. Line a loaf pan with parchment paper. Melt the butter in a large skillet. Add the chopped onion and saut until soft and golden. Add the frozen corn and the evaporated milk and simmer for 3-5 minutes. Remove from heat. Stir in the corn meal and cheese and mix well. Stir in the egg yolks. Taste for salt and pepper and season to taste. In a clean bowl, beat the egg whites until stiff peaks form. Gently fold the egg whites into the batter, until just barely mixed. Spoon batter into the loaf pan. Bake for 30-40 minutes or until done. You should bake until corn bread is golden brown and springs back slightly when pressed. Remove from the oven and let cool in the pan.